1. Field of the Invention
The present invention relates, generally to medical devices. More particularly, the invention relates to vaso-occlusion devices used in radiology and embolotherapy.
2. Background Information
In embolotherapy, it is often desirable to occlude blood flow in a section of vasculature for purposes such as controlling internal bleeding, stopping blood supply to tumors, and relieving vessel-wall pressure in a region of a vessel aneurysm. Numerous devices have been developed for this purpose. U.S. Pat. No. 4,994,069 describes devices and methods such as cross-linking liquids, cyanoacrylate resins, balloons and helical wire coils. Helical coils found favor, but because they are dimensioned to engage the walls of the vessel, they are relatively stiff and difficult to advance through a catheter.
The device of U.S. Pat. No. 4,994,069 provides a smaller coiled wire that, when tensioned, would have a linear configuration allowing it to easily be advanced through a catheter to the desired site. When the wire exits the catheter, it relaxes and takes a random convoluted shape to form a space-filling mass lodged in the vessel at the site of release. However, because the final shape of the relaxed coil in the blood vessel is random, the precise location and specific length the device occupies in the vessel cannot be guaranteed.
Another problem with wire coils is providing enough occlusion to allow a blood clot to form. A partial solution is to coat the wire with fibers such as dacron or cotton, but recanalization can occur by resorption of the clot by endothelial cells. The fiber coating also increases the friction between the coated wire and the catheter making it more difficult to advance the coils through the catheter. Another way to combine fibers and coiled wire is disclosed in U.S. Pat. No. 5,226,911 where flexible fiber loops extend outward from windings of the coil at regular intervals.
An alternative to helical wire coils is tubular braided devices made from radiopaque fibers or wires as disclosed in U.S. Pat. No. 5,423,849. These braided structures are significantly smaller than the vessel into which they are to be introduced, so they could easily be pushed through a catheter. The tubular structure could be straight, or convoluted into a variety of shapes such as a circle, a "C" or a figure "8". Typically a plurality of devices are introduced at a site in the vasculature. The braided wires may have additional fibrous elements attached to them to increase the occludability of the device.
Another braided structure is disclosed in U.S. patent application Ser. No. 08/608,110, titled Self Expanding Vascular Occlusion Device, filed on Feb. 28, 1996. A braided tubular structure is compressed axially, which expands it diametrically. The structure is then heat-set in that shape. In one embodiment, the expanded portion is heat-set in the form of a disk. In another embodiment the device has two sections, each forming a disk which is then shaped into a cone, the final heat-set shape being similar to two cones attached end to end. One of these devices is straightened to its cylindrical braided form to advance it through a catheter. When it exits the catheter, the device returns to its formed shape and lodges in the blood vessel. Additional fibrous material may be attached inside the core of the device to improve its occludability.
Vascular occlusion with all of these devices depends on the flow of blood being restricted enough by the presence of a large quantity of fibrous material in the blood stream. Initial deployment of such devices significantly reduces blood flow, but flow may not completely stop. Clots soon form in the deployed device or devices which further reduce blood flow. Blood flow eventually may be completely stopped by the device. This takes time. The effectiveness of such occlusion may also be quite variable. It is desirable for a vascular occlusion device to be self-expanding, accurately positionable, and to completely occlude a blood vessel immediately upon deployment.
Despite the need in the art for a vascular occlusion device which overcomes the disadvantages, shortcomings and limitations of the prior art, none insofar as is known has been developed.